1. Field of the Invention
The present invention relates to the field of tyrosinase inhibitors and to methods and compositions of treatment involving inhibition of this enzyme.
2. Related Art
The present invention relates to novel biological agents, specifically oligopeptides that reduce the enzymatic activity of tyrosinase. These agents have use as research and development tools in basic science investigation, in diagnostic applications, as cosmeceuticals for the treatment of skin conditions characterized by hyperpigmentation, and as therapeutics for the treatment of pathological conditions that rely on tyrosinase enzyme activity to promote their tumorigenicity.
Melanin plays an important role in protecting the human body from the harmful effects of ultraviolet rays. Melanin is also an important factor in medical science and cosmetology. It is known that melanin is formed or synthesized in skin tissues. Excessive amounts of melanin darken the skin, and the nonuniform distribution of melanin causes chloasma and ephelis, both of which are skin disorders. The biosynthesis pathway of melanin involves the catalytic hydroxylation of tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA) and the conversion of L-DOPA to dopachrome. An effective way to inhibit the synthesis of melanin is to block the hydroxylation of tyrosine.
Hydroquinone (HQ) has been used since the 1950s in commercially available over-the-counter skin lightener products and since the 1960s as a commercially available medical product. It is also used in cosmetic products such as hair dyes and products for coating fingernails. Beginning in 2001, HQ is no longer authorized for use in cosmetic skin lightening formulations in European Union countries, although products containing arbutin, an analogue of HQ, and botanicals, including plants that naturally contain HQ and arbutin, continue to remain available in European countries See also, Matsubayashi et al., “Pharmaceutical and clinical assessment of hydroquinone ointment prepared by extemporaneous nonsterile compounding,” Biol Pharm Bull. 2002 January; 25(1):92-6. As disclosed there, ointments of the skin depigmentation agent hydroquinone (HQ) have been prepared by extemporaneous nonsterile compounding in Japan by imitating skin lightening creams commercially available in the U.S.A. and European Union. However, various problems have been observed including chromatic aberration of HQ ointments, relatively large variability of efficacy, and undesirable side effects although they were mild. HQ has a published IC50 of about 700 μM.
Therapies containing hydroquinone have been outlawed in Asian countries, making the standard HQ treatment inaccessible to a large number of people suffering from this condition. In fact, the United States FDA has issued a notice indicating that it may too ban the use of hydroquinone domestically. Furthermore, hydroquinone has been associated with visceral malignancy and long-term topical delivery may be a potentially harmful therapeutic option. Hydroquinone in the best of circumstances leads to only a partial alleviation of hyperpigmentation. Some cosmeceutical formulations have included other active ingredients such as kojic acid, arbutin, and vitamin C but efficacy has thus far been disappointing due to problems with chemical instability or inability to deliver the active to the appropriate layer of skin. Although higher concentrations have been utilized, patients often discontinue treatment due to skin irritation. This led to the addition of topical steroids in order to reduce irritation from the active ingredients such as retin A and hydroquinone. Since melasma and other hyperpigmentary disorders often take months to years to treat, use of topical steroids on the face at the strength required to combat irritant effects of active ingredients is not possible without causing topical steroid-induced side effects. When medium or greater potency topical steroids are used on the face for more than several weeks consecutively, skin atrophy, fragility and telengiectasia commonly occur. This side effect profile is unacceptable, especially in areas such as the face.
Infrared lasers have been used with some success. They generally are more effective for conditions that localize pigment to the deeper skin areas such as the dermis. In order to effectively treat the epidermis, an ablative treatment is usually employed. This therapy is associated with significant downtime for the patient, including creation of second-degree burn or erosion leaving the patient susceptible to infection. In addition, laser therapy is an expensive treatment option that many patients cannot afford. In extreme cases, depigmentation of the skin has been elected when bleaching agents have been unsuccessful. Numerous pathological conditions can lead to the deposition of pigment into the skin aberrantly. For example, it is well known that hormonal imbalance can cause facial and extremity hyperpigmentation, most frequently observed in women during or following pregnancy. Often times, this hyperpigmentation becomes aesthetically disfiguring, leading to problems with self-esteem and embarrassment in social situations. Melasma often times affects individuals with Fitzpatrick type IV-VI skin. This constitutes a significant portion of the worldwide population.
A large number of individuals with Fitzpatrick type IV to VI skin are of Asian descent.
According to the Fitzpatrick skin type scale, based on a test of appearance and skin reaction to sun exposure, individuals are generally categorized as follows:
Type I: Very fair skin tone, blond or redhead,
Type II: Light skin tone, will tan, but usually burns.
Type III: White to olive skin tone, sometimes burns.
Type IV: Medium brown skin tone, rarely burns.
Type V: Dark brown skin tone, very rarely burns.
Type VI: Black skin tone, very dark eyes, burn resistant.
In addition to melasma, hyperpigmentation of aesthetically sensitive locations such as the face may take place after inflammation due to disorders such as acne or rosacea, amongst others. These conditions may also lead to significant psychological discomfort. In the United States, $13 billion are spent on cosmeceuticals each year. With the anticipated ban of hydroquinone in the US market, in conjunction with the continued stability (vitamin C) or delivery (arbutin, kojic acid, etc) problems of other non-pharmacological agents currently on the market, oligopeptide inhibitors may provide a solution to this large unmet need.